[unreadable] Genomic stability depends on faithful replication, accurate repair, and precise inheritance. The maintenance of an intact mitochondrial genome is of critical importance for viability or competitiveness of virtually all eucaryotic cells. In humans, mutations of tRNA, rRNA, and structural genes present in mitochondrial genomes result in severe genetic diseases, and the accumulation of deletions in mitochondrial DNA is linked to aging. However, under appropriate culture conditions, both human cells and the yeast Saccharomyces cerevisiae can grow without mitochondrial DNA. The general goal of the research effort proposed here is to understand the genetic and biochemical requirements for growth of eucaryotic cells in the absence of mitochondrial DNA. It has been hypothesized that the ability of these cells to grow without mitochondrial DNA is dependent upon the exchange of ATP (-4 charge) for ADP (-3 charge) across the mitochondrial inner membrane via the adenine nucleotide translocator, thus creating the essential membrane potential. A corollary of this hypothesis is that the exchange of ATP for ADP must occur with enough frequency to assure formation of a membrane potential of sufficient magnitude, and the rapid conversion of ATP to ADP via the action of F1-ATPase assures adequate flux through the adenine nucleotide transporter. Analysis of mutations in yeast that prevent growth in the absence of mitochondrial DNA has been the basis for the formulation of this model. However, critical aspects of the model remain untested. Additionally, data indicating a role for mitochondrial gene products in maintaining viability when the exchange of ATP for ADP is blocked, which is not part of their classic biochemical roles in oxidative phosphorylation, remain unexplained. Consequently, experiments have been designed to critically test: 1). the role ATP hydrolysis in the mitochondrial matrix plays in the generation of the essential membrane potential; 2). the role of established and novel regulators of F1Fo-ATPase in the establishment of the potential across the inner mitochondrial membrane; 3). the identity of the mitochondrially encoded gene products required in cells lacking the adenine nucleotide translocator. [unreadable] [unreadable]